Patent GB-780075-A (GB)
Title: Improvements in and relating to injection moulding machines
IPC: B29C45/67
Filed: 1954-08-20
Abstract: 780,075. Injection-moulding machines. CROWN MACHINE & TOOL CO. Aug. 20, 1954, No. 24353/54. Class 87(2). The hydraulic pump motors which operate the machines are started and a timer switch 109 is closed to allow the necessary time for the heating elements to become heated. A master relay 127 operates a solenoid pilot valve 128 and causes hydraulic fluid to enter a cylinder 46 and force a piston 48, through its piston rod 38, to move a platen member 18, carrying a piston 20, Fig. 8, and to move a platen 12, carrying one mould member towards a fixed platen 6 to which is secured the other mould member. The platen member 18 is attached to the platen 12 by a loop linkage. A limit switch 136 operates a solenoid valve 84 to cause fluid from a medium pressure pump 88 to enter a cylinder 68 and force a piston 66 to rotate a thrust plate 72 into a position where lugs on its periphery move from behind the ends of compression bars 74 projecting from the platen member 18 so that the thrust plate forms a distance piece between the platen and a backing support 14. At the end of its movement the plate 72 trips a limit switch 80 which causes a solenoid valve 160 to direct fluid from a high pressure pump 90 to the cylinder 22 in the platen 12 into which fits the piston 20, so exerting a high mould closing pressure. When the back pressure has built up to a certain value it operates a valve 178 which directs hydraulic fluid from the pump 90 (through conduits 162, 176) to a hydraulic ratio booster pump 188 which discharges hydraulic fluid under increased pressure into the cylinder 22 to give a final squeeze in closing the mould. The pressure in the cylinder 22 operates a pressure switch 200 which operates a relay 207 which energizes the solenoid 203 of a four-way valve 205 which shifts valve mechanism so that fluid from the pump 88 is led to a pressure accumulator 246. When the pressure has risen to a definite value a double pressure port valve 240 opens a sequence valve 251 which directs fluid from the pump 88 to a cylinder 222 to advance the injection plunger 260 for the injection of molten plastic material into the mould. The valve 240 also directs fluid to a cylinder 254 to open the injection nozzle. The switch 200 also operates a relay 204 which sets an electronic timer 208 to control the lapse of time before the valve 160 operates to allow fluid to escape from the cylinder 22 to a value at which the switch 200 operates to de-energize the relays controlled by it. The electronic timer holds in the plunger 260 long enough for the plastic material to cool in the mould and then actuates a solenoid control valve 205 to discharge the hydraulic fluid in the valve 240 back to the reservoir. The timer also, at the end of this lapse of time, deenergizes a relay which causes the valve 84 to operate and reverse the flow of hydraulic fluid to the cylinder 68, so causing the piston 66 to retract and withdraw the thrust plate 72, unlocking the platens. The thrust plate 72, at the end of its travel, trips a limit switch 82, de-energizing the solenoid valve 128 which in turn causes a valve 118 to direct fluid to the cylinder 48 so as to retract the-piston 48 and move the platens 18, 20 to the mould-open position. The moulded article is ejected by rods (not shown). At the end of its travel a cam 138 on a bar 64 attached to the platen member 18 trips a limit switch 134 which starts a " mould-open " time interval in the electronic timer, at the conclusion of which it operates to restart the cycle. A pre-plasticizing unit 210 is incorporated in which a fluid-operated piston 212 in a cylinder 214 feeds granular plastic material from a hopper 216 into a chamber 218, where it is melted, being injected by the plunger 260 in the molten state. The piston 212 is reciprocated by the combined action of a pilot valve 220 and a switching valve 232, the pilot valve directing fluid alternately to opposite ends of the valve 232- and the valve 232 directing fluid alternately to conduits 234 and 236 leading to opposite ends of the cylinder 214. The injection cylinder, injection nozzle and preplasticizing unit are mounted on a movable bed plate 308, which can be withdrawn by a crank 312 operating a screw to render them accessible. Access to the other end of the machine is through a door 298 on which is fitted a cam which operates a valve 140 to cause the piston 48 to move back and open the mould, if closed, when the door is opened. When the piston 48 is retracted a nut 36 on the piston rod 38 moves the ends 32 of a pair of members which are attached by clevises to rods 24 threaded into the piston 20 and passing through the platen member 18. As seen from Fig. 11, which shows one of the members, the movement causes the ends 30 to engage the rear face of the member 18 and move it to expel hydraulic fluid from the cylinder 22. The-weight of large mould members is taken, through jack screws, by a bridge piece which spans the distance between extensions 10 from the platen 12. Tie rods 16 pass through the stationary platen 6 and back-up member 14 and are secured by nuts 17. Being in tension when the mould is closed the tie rods ensure the effectiveness of the final mould squeezing action, and by means of the nuts 17 the relative position of the platen 6 and back-up member 14 is adjustable to accommodate mould members of various sizes and the opening between them. For the same purpose the position of the cam 138 on the bar 64, which operates the limit switch 136, is adjustable. Another cam 62 on the bar 64 actuates a travel limiting valve 146 should the limit switch fail to operate and prevents damage to the machine.